Enzymes

1. Enzymes Any chemical reaction requires a certain amount of energy to begin. This energy is called “Activation Energy” or EA A large EA means that the reaction will take place very slowly. To increase the rate of the reaction, heat can be added to reach the EA. In the cells of biological systems, proteins would be damaged if excessive heat is added. B1.1, B2.1, B3.5

2. Enzymes: molecules that catalyze reactions in living cells • most are proteins • lower the activation energy required for a reaction • are not changed or consumed by the reaction • are very specific E.g. Enzyme (carbonic anhydrase) catalyzes the reaction of CO2 and H2O into carbonic acid at a rate of 600 000/second! B1.1, B2.1, B3.5

3. B1.1, B2.1, B3.5

4. Enzymes interact with substrates. substrate: molecule that will undergo a reaction active site:region of the enzyme that binds to the substrate Binding of an enzyme to a substrate causes the enzyme to change shape, producing a better induced fit between the molecules. “Enzyme-substrate complex” B1.1, B2.1, B3.5

5. B1.1, B2.1, B3.5

6. Enzymes can shape slightly to accommodate the substrate in the A.S.: “Induced fit” B1.1, B2.1, B3.5

7. Some enzymes require additional molecules for proper enzymatic activity. These molecules could be: -cofactors: usually metal ions (e.g. Fe, Zn), found in the active site participating in catalysis -coenzymes: nonprotein organic molecules, often used as an electron donor or acceptor in a redox reaction B1.1, B2.1, B3.5

8. Naming: • May be named after the type of reaction they catalyze • E.g. Those that catalyze hydrolysis reactions: hydrolases • Usually have “-ase” ending -E.g. Sucrase-catalyzes the reaction of sucrose to glucose and fructose B1.1, B2.1, B3.5

9. Enzymes Enzyme function is affected by its environment. Factors that can change an enzyme’s 3-dimensional shape can change its function. -for example, pH, temperature, regulatory molecules B1.1, B2.1, B3.5

10. Factors Affecting Rate of Reaction Temperature -enzyme activity may be increased with increasing temp, up to the temp optimum -temperatures too far above the temp optimum can denature the enzyme, destroying its function pH – most human enzymes prefer pH values from 6 to 8 Substrate Concentration -low amount of substrate makes it difficult for Ez & substrates to encounter each other. Therefore Ez activity inc. as substrate conc. inc. -works to a point. B1.1, B2.1, B3.5

11. B1.1, B2.1, B3.5

12. Inhibitors are molecules that bind to an enzyme to decrease enzyme activity. Decrease its ability to interact with its substrate. -competitive inhibitors compete with the substrate for binding to the same active site -noncompetitive inhibitors bind to sites other than the enzyme’s active site B1.1, B2.1, B3.5

13. B1.1, B2.1, B3.5

14. Many enzymes also have an allosteric site-site away from the active site that will alter the activity of the enzyme (change 3D shape). This is a type of non-competitive inhibition. Allosteric enzymes exist in either an active or inactive state. -allosteric inhibitors bind to the allosteric site to inactivate the enzyme allosteric activators bind to the allosteric site to activate the enzyme B1.1, B2.1, B3.5

15. B1.1, B2.1, B3.5

16. Many biochemical reactions are grouped together in pathways. Biochemical pathways are a series of reactions in which the product of one reaction becomes the substrate for the next reaction. B1.1, B2.1, B3.5

17. B1.1, B2.1, B3.5

18. Biochemical pathways are often regulated by feedback inhibition in which the end product of the pathway is an allosteric inhibitor of an earlier enzyme in the pathway. B1.1, B2.1, B3.5

19. B1.1, B2.1, B3.5

20. Homework: • P41 #1,2 (Fabry Disease Reading) • P42 #3,6,8-12 B1.1, B2.1, B3.5